This application relates generally to communication systems, and, more particularly, to wireless communication systems.
Wireless communication systems include a network of devices for providing wireless connectivity to wireless-enabled devices including mobile units, smart phones, tablet devices, laptops, desktops, and other types of user equipment. Network architectures generally fall into two broad categories: hierarchical and distributed. Hierarchical network architectures used centralized entities to handle mobility management and radio resource control. For example, in conventional hierarchical communications, a server transmits voice and/or data signaling destined for a target access terminal to a central element such as such as a Radio Network Controller (RNC). The RNC may then transmit paging messages to the target access terminal via one or more access nodes to locate the target access terminal. The target access terminal may establish a communication link to one or more of the access nodes in response to receiving the page from the network. A radio resource management function within the RNC receives the voice and/or data signaling and coordinates the radio and time resources used by the set of access nodes to transmit the information to the target access terminal. The radio resource management function can perform fine grain control to allocate and release resources for broadcast transmission over a set of access nodes.
In contrast, a distributed network includes access points that implement distributed communication network functionality. For example, each distributed access point may combine part or all of the RNC and/or Packet Data Serving Node (PDSN) functions in a single entity that manages radio links between one or more access terminals and an outside network, such as the Internet. Distributed access points may implement proxy functionality that utilizes core network element support to equivalent IP functions. For example, IP anchoring in a UMTS base station router may be offered through a Mobile IP Home Agent (HA) and the Gateway GPRS Support Node (GGSN) anchoring functions that the base station router proxies through equivalent Mobile IP signaling. Compared to hierarchical networks, distributed architectures have the potential to reduce the cost and/or complexity of deploying the network, as well as the cost and/or complexity of adding additional access points to expand the coverage of an existing network. Distributed networks may also reduce (relative to hierarchical networks) the delays experienced by users because packet queuing delays at the RNC and PDSN of hierarchical networks may be reduced or removed.
At least in part because of the reduced cost and complexity of deploying a base station router, base station routers may be deployed in locations that are impractical for conventional base stations. For example, a base station router may be deployed in a residence or building to provide wireless connectivity to the occupants of the residents or the building. Base station routers deployed in a residence are typically referred to as home base station routers or femtocells because they are intended to provide wireless connectivity to a small area that encompasses a residence. Home base station routers may also be referred to as microcells, picocells, small cells, and the like. However, the functionality in a home base station router is typically quite similar to the functionality implemented in a conventional base station router that is intended to provide wireless connectivity to a macro-cell that may cover an area of approximately a few square kilometers. One important difference between a home base station router and a conventional base station router is that home base station routers are designed to be plug-and-play devices that can be purchased off-the-shelf and easily installed by a lay person.
As communication networks grow and evolve, they incorporate numerous types and generations of wireless communication systems that provide network connectivity according to different standards and/or protocols. Networks that implement different types of access devices that operate according to different standards and/or protocols are typically referred to as heterogeneous networks. Exemplary heterogeneous networks include systems that provide wireless connectivity to femtocells (e.g., systems that provide wireless connectivity according to the IEEE 802.11, IEEE 802.15, or Wi-Fi standards) and systems that provide wireless connectivity to macrocells (e.g., systems that operate according to the Third Generation Partnership Project standards—3GPP, 3GPP2—and/or systems operate according to the IEEE 802.16 and IEEE 802.20 standards). Multiple generations of these systems have been deployed including Second Generation (2G), Third Generation (3G), and Forth Generation (4G) standards.
The coverage provided by different service providers in a heterogeneous communication system may intersect and/or overlap. For example, a wireless access node for a wireless local area network may provide network connectivity to mobile nodes in a femtocell, microcell, or picocell associated with a coffee shop that is within the macrocell coverage area associated with a base station of a cellular communication system. For another example, cellular telephone coverage from multiple service providers may overlap and mobile nodes may therefore be able to access the wireless communication system using different generations of radio access technologies, e.g., when one service provider implements a 3G system and another service provider implements a 4G system. For yet another example, a single service provider may provide coverage using overlaying radio access technologies, e.g., when the service provider has deployed a 3G system and is in the process of incrementally upgrading to a 4G system.
Transmissions into overlaying coverage areas may interfere with each other. For example, downlink signals transmitted by a macrocell are often stronger than the downlink signals transmitted by picocells in portions of the overlaying coverage area of the picocell. User equipment being served by the picocells may therefore receive strong interfering signals from the macrocell, which can dramatically reduce the signal to noise ratio for the user equipment. Intercell interference coordination (ICIC, eICIC) can be used to reduce or mitigate this interference. For example, almost blank subframes (ABS) can be defined during one or more subframes. The macrocell bypasses transmission of downlink traffic during the almost blank subframes to reduce interference for user equipment that are currently being served by the overlaying picocells. However, the standards governing allocation of the almost blank subframes lack clarity and do not provide adequate mechanisms for supporting efficient and dynamic ABS algorithms.